Climate change is shifting long-term mean values of environmental drivers like temperature and precipitation, but it is also changing their variability. Changes in the long-term variability of precipitation and wind can manifest as stronger storm systems which occur more frequently and with greater intensity than they did in the past. Increasingly extreme storm events can affect how we normally view aquatic ecosystem function through forcings associated with precipitation, wind, or a combination of both. For example, strong wind events may mix the water column of lakes, suspending sediments and altering the availability of nutrients and light, while heavy precipitation can bring influxes of nutrients from the watershed or cause flooding. Streamflow may drastically increase in response to extreme precipitation, bringing with it large flows of solutes, particulate matter, and sediment. In coastal ecosystems, storms can disturb aquatic habitat and organisms while also altering the physical and chemical characteristics of the system. Understanding the current response of aquatic ecosystems to storms is crucial if we want to better predict how increasingly extreme storms will affect aquatic ecosystems in the future. We welcome any contributions focused generally on the effects of storms on aquatic ecosystems, including their physical, chemical, and biological responses. We are particularly interested in studies which place the effects of storms into a broader context of global climate change.
Lead Organizer: Daniel Szydlowski, Center for Limnology, University of Wisconsin-Madison (dszydlowski@wisc.edu)
Co-organizers:
David Ortiz, Center for Limnology, University of Wisconsin-Madison (dortiz4@wisc.edu)
Presentations
09:00 AM
AQUATIC HEATWAVES INCREASE PRIMARY PRODUCTION IN THREE NORTH TEMPERATE LAKES (7896)
Primary Presenter: Daniel Szydlowski, Center for Limnology (dszydlowski@wisc.edu)
Widespread eutrophication of inland waters is interacting with changing temperatures globally, potentially altering algal production and resulting in harmful blooms. While increases in mean water temperature are linked to enhanced primary production, it is unclear how discrete weather extremes like heatwaves alter phytoplankton dynamics in lakes. Heatwaves may increase phytoplankton production by enhancing photosynthesis and growth, but could drive declines in phytoplankton if extreme temperatures cause damage to individual cells or disproportionately increase respiration. We investigated changes in phytoplankton biomass following 27 summer heatwaves between 2008-2019 in three north temperate lakes located in Michigan, United States using daily summer measurements of surface chlorophyll a. These lakes vary in water color and two of the lakes were experimentally enriched with nutrients in some years of the study period, offering a unique opportunity to study the effects of heatwaves on phytoplankton under a variety of nutrient and light conditions. On average, aquatic heatwaves in the study lakes increased phytoplankton biomass by 57%, but the magnitude of change due to the heatwaves varied by year, lake, and event. For example, the low-nutrient reference lake had a lower mean increase in chlorophyll following heatwaves (31%) than either of the nutrient addition lakes (69%, 97%). Our results suggest that the interacting effects of other global change drivers such as eutrophication and brownification will help shape the response of phytoplankton to extreme heat events.
09:15 AM
INFLUENCE OF PRECIPITATION ON THE SPATIAL DEVELOPMENT OF ALGAE IN A LARGE EUTROPHIC LAKE (8278)
Primary Presenter: David Ortiz, University of Wisconsin - Madison (dortiz4@wisc.edu)
The upper Midwestern U.S. is experiencing more intense rain events, leading to greater runoff events, and potentially increasing the risk of eutrophication in lakes. Despite advancements provided by buoys, they do not capture spatial variability of algal blooms. Algal blooms on lake surfaces are notoriously heterogenous and can be underestimated or missed if monitoring efforts occur at a single location. We conducted a comprehensive study in Lake Mendota, WI, a eutrophic lake, to investigate the influence of precipitation events on nutrient inputs, and chlorophyll a concentration. We compared chlorophyll fluorescence collected through time at a centralized buoy and spatially across the entire lake surface using a mobile sampling boat on 45 occasions in 2016 and 2022. While precipitation events were hypothesized to enhance nutrient influx and stimulate algal growth, we observed increases, decreases, and no changes in chlorophyll a concentrations, following different rain events. Notably, the two major inlets exhibited little or no positive correlation in N:P ratios or algal concentrations, highlighting effects of different land uses on nutrient dynamics. Moreover, the buoy failed to capture the full range of chlorophyll concentrations in the lake during two relatively low production years. This counterintuitive result underscores the complexity of lake ecosystems and emphasizes the need for spatially comprehensive monitoring approaches, especially given ongoing changes in precipitation trends increasing the risk of eutrophication and the heterogeneity of bloom development.
09:30 AM
SHORT- AND LONG-TERM EFFECTS OF HURRICANES ON LAKE OKEECHOBEE WATER QUALITY AND CYANO-HABs (8259)
Primary Presenter: Anna Wachnicka, South Florida Water Management District (awachnic@sfwmd.gov)
Hurricanes are natural disturbance events that have a significant impact on aquatic systems by drastically changing their biogeochemistry, habitats, and geomorphology. Understanding the impacts of individual hurricanes and the cumulative impacts of recurring hurricanes is essential for managing these systems. A series of hurricanes that impacted Florida provide a unique opportunity to explore the direct and indirect effects that these extreme events have on Lake Okeechobee’s water quality and cyano-HABs. Since the 1800s, the lake has been impacted by 17 major hurricanes, with 3 directly crossing the lake. Hurricanes Frances and Jeanne (2004), Wilma (2005), Irma (2017), and Ian and Nicole (2022) caused significant alteration of the lake’s water quality, sediment distribution and thickness, cyano-HAB dynamics, and vegetation cover. High winds generated by these events produced large seiches, and strong waves and currents, which eroded and redistributed bottom sediments and uprooted aquatic vegetation in the littoral zone. The large transport of suspended particles and nutrients from the surrounding watershed further exacerbated water quality issues in the lake. These poor water quality conditions lasted more than 4 years following hurricanes Frances, Jeanne, and Wilma, and for at least 3-6 months following hurricanes Irma, Ian, and Nicole. Significant reduction of water column transparency inhibited phytoplankton growth directly after the hurricanes, but high external and internal nutrient inputs during the events often resulted in extensive cyano-HABs in the following years.
09:45 AM
INVESTIGATING THE INTERPLAY BETWEEN WATER LEVELS AND CLARITY IN NINE NORTHWEST WISCONSIN LAKES OVER MULTIPLE YEARS (8120)
Primary Presenter: Cayla Cavey, Mary Griggs Burke Center for Freshwater Innovation (ccavey@northland.edu)
Precipitation is a primary contributor to lake water level fluctuation across seasonal and annual timescales. Runoff attributable to precipitation is expected to decrease water clarity as organic compounds, nutrients, and sediment enter a lake. Therefore, water clarity is expected to decrease as water levels increase. We investigated the interplay of water level fluctuation, water clarity, and algal abundance amongst nine lakes in northwestern Wisconsin. Lake morphometry and dissolved organic matter concentrations varied between the study lakes, whereas precipitation was likely similar across all lakes given their close proximity on the landscape. Lake stage and light attenuation (photosynthetic active radiation and Secchi depth) were used to evaluate the association between lake level and water clarity with measurements from the open water period over 5-9 years. In general, water clarity decreased as water levels increased. However, the extent to which water clarity changed varied between clear and stained lakes. For example, a greater shift in light attenuation (1.9-4.3 m-1) occurred in a stained lake with less water level fluctuation (0.8 m) than a clear-water lake, which had less light attenuation (0.4-0.9 m-1) despite a larger change in water level (1.1 m). Oscillations in water clarity as a result of water level variation may affect lake food web dynamics across trophic levels. The results of our study will support the development of well-informed management decisions, particularly as global climate change affects precipitation event frequency and intensity.
10:00 AM
The Magnitude and Transformation of Resuspended Phosphorus in Western Lake Erie (8340)
Primary Presenter: Connor Gluck, Cooperative Institute of Great Lakes Research (cgluck@umich.edu)
Due to the history of eutrophication, there is potentially a large pool of phosphorus (P) in the sediment of Lake Erie that can be mixed into the water column by strong winds and currents. The magnitude and bioavailability of resuspended P, as well as its fate following resuspension, is poorly understood. To investigate this, we performed controlled resuspension experiments using sediment cores from three sites in Lake Erie’s western basin. We sampled water for seven P fractions at four intensities of shear stress and found that the majority of resuspended P was in particulate forms that are less bioavailable. The highest shear stress measured would increase water column TP concentrations by 1.7-12.1 ug P/L depending on the site but only increase bioavailable P concentrations by 0.96-2.6 ug P/L. To examine the short-term fate of this material, we incubated resuspended sediment diluted into lake water for 48 hours while mixing. Concentrations of P forms were stable over 48 hours following resuspension, suggesting that sorption-desorption processes do not play a large role in changing net bioavailability of P. These findings are important for determining how sediment resuspension may affect quantity and bioavailability of P in western Lake Erie.
10:15 AM
COLLOIDAL PHOSPHORUS TRANSPORT DURING STORM EVENTS IN THE MAUMEE RIVER WATERSHED (8236)
Primary Presenter: Ashlynn Boedecker, Ohio State University (boedecker.4@osu.edu)
One important driver of eutrophication in aquatic ecosystems is bioavailable P loading. The most abundant form of bioavailable P is soluble reactive P (SRP), which is commonly assumed to be all phosphate even though standard methods measure any P molecule which passes through a 450 nm filter and binds with molybdate under acidic conditions. In lotic systems, colloidal particles (~5 – 450 nm) can be important inorganic and organic P carriers; however, the bioavailability of colloidal P can be lower than phosphate, suggesting that we may overestimate bioavailable P concentrations when colloidal-SRP is high. Thus, it is important to understand the spatial and temporal patterns in colloidal-SRP concentrations. Since colloid exports from agricultural systems are generally highest following a drying-rewetting cycle, and one of the effects of climate change in the Midwest U.S. is stronger storms with higher rainfall amounts, we predicted that stream colloidal-SRP concentrations would be highest during storm events. We combined biweekly monitoring of three streams with storm event sampling in 12 different tributaries throughout the Maumee River watershed (NW Ohio). We measured dissolved and colloidal-SRP, along with the concentrations of potential P-binding elements and compared it to periods of no rainfall. The fraction of SRP in the colloidal fraction was very low during low to moderate flow periods, but higher during storm events. Understanding the spatiotemporal variation in colloidal P concentrations will advance our knowledge of P cycles and improve eutrophication management.
SS13 - Navigating Stormy Waters: Understanding the Response of Aquatic Ecosystems to Storms in a Changing Climate
Description
Time: 9:00 AM
Date: 3/6/2024
Room: Hall of Ideas G